Pipi, also called Pipiko, is the sole surviving mermaid after the Poseidon family exterminated her Triton clan 5,000 years ago out of envy over their prosperity in Atlantis. She remained concealed until encountering Triton during his quest for vengeance against Poseidon. Pipi allies with him in his war against Poseidon and his forces, battling Poseidon's offspring through a partnership forged by mutual survival and retribution.

After eliminating Poseidon's children and securing a truce mediated by the ancient turtle Ganomosu, Pipi marries Triton. She lays seven eggs that hatch into two sons and five daughters: Blue, Green, Indigo, Yellow, Orange, Red, and Violet Triton. Pipi helps raise them on Ganomosu's shell-formed floating island. When a storm scatters the family during Triton's educational sea voyage with the children, Green Triton is captured by humans. This triggers Triton's journey to land, where Poseidon frames him for attacking Tokyo with tsunamis. After Triton exposes the frame-up with human aid, he departs for a final confrontation with Poseidon, appointing Blue Triton as the mermaid family's leader.

Following Triton's death in the climactic battle at Poseidon's base, Pipi guides her children to the dying Ganomosu. The turtle transforms his body into a permanent island sanctuary where Pipi and her offspring establish their home, securing their lineage's future away from Poseidon's threats and humanity.